The answer is to create a VPC Gateway Endpoint for S3 and attach it to the private subnet route tables. This is the most cost-effective and secure way to access S3 from private subnets because a Gateway Endpoint uses AWS’s private network backbone, bypassing the public internet entirely, and incurs no hourly charges or data processing fees—unlike a NAT Gateway, which adds both cost and complexity. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of VPC endpoints and cost optimization, often appearing as a trap where candidates mistakenly choose a NAT Gateway for private subnet connectivity. The key distinction is that S3 and DynamoDB support Gateway Endpoints, which are free and route traffic via prefix lists, while all other AWS services require Interface Endpoints or a NAT device. Memory tip: think “Gateway for S3—free and private, no NAT to complicate.”
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company has a VPC with public and private subnets in two Availability Zones. The company hosts a web application on EC2 instances in the private subnets. The application needs to access an S3 bucket. What is the MOST cost-effective and secure way to provide this access?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a VPC Gateway Endpoint for S3 and attach it to the private subnet route tables.
Option A is correct because a VPC Gateway Endpoint for S3 provides private connectivity without traversing the internet, and it is free of charge (no data transfer costs). Option B is wrong because a NAT Gateway incurs hourly charges and data processing fees. Option C is wrong because a Transit Gateway is not needed for a single VPC. Option D is wrong because an Internet Gateway exposes traffic to the internet and would require public IPs or NAT, increasing cost and risk.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Deploy a NAT Gateway in each public subnet and route traffic from private subnets through it.
Why it's wrong here
Incurs hourly and data processing charges.
✗
Use AWS Transit Gateway to route traffic to S3 via a centralized VPN.
Why it's wrong here
Over-engineered and costly for a single VPC.
✗
Attach an Internet Gateway to the VPC and assign public IPs to the EC2 instances.
Why it's wrong here
Exposes instances to the internet, less secure.
✓
Create a VPC Gateway Endpoint for S3 and attach it to the private subnet route tables.
Why this is correct
Cost-effective and secure; no data transfer costs.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create a VPC Gateway Endpoint for S3 and attach it to the private subnet route tables. — Option A is correct because a VPC Gateway Endpoint for S3 provides private connectivity without traversing the internet, and it is free of charge (no data transfer costs). Option B is wrong because a NAT Gateway incurs hourly charges and data processing fees. Option C is wrong because a Transit Gateway is not needed for a single VPC. Option D is wrong because an Internet Gateway exposes traffic to the internet and would require public IPs or NAT, increasing cost and risk.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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